The present invention relates to the maintenance of a set of equipment, such as the set of avionic equipment of an aircraft which fulfill the various functions required for accomplishing a flight.
An aircraft comprises a large number of pieces of equipment, of diverse kinds, mechanical, hydraulic, electrical or electronic, whose proper operation is essential during a flight.
To improve the degree of confidence accorded to these pieces of equipment, a monitoring of their proper operation is carried out for each of them as often as possible, consisting of a monitoring of the fundamental parameters and within automatic or semiautomatic tests of proper operation, followed by a fault diagnosis which may lead to the issuing of fault messages. This monitoring of proper operation, associated with a piece of equipment, is known as the BITE function, stemming from the abbreviation for the expression “Built In Test Equipment”.
The BITE function of a piece of equipment is assumed by a piece of electronics which may be specific or shared with other functions of the relevant piece of equipment. This piece of electronics performs the software processing required by the BITE function. It comprises a greater or lesser hardware part integral with the piece of equipment, with, as a minimum, in this hardware part, a nonvolatile memory in which are stored the violations of specification by the monitored parameters, the results of the tests, the fault diagnosis when it exists as well as the fault messages issued. The fault messages of the BITE functions of the monitored pieces of equipment of an aircraft are addressed, via an airplane data transmission link, to a centralizing piece of equipment placed on board the aircraft so as to gather the various fault messages issued.
On board recent aircraft, the fault messages originating from the BITE functions of the various pieces of equipment are consultable from the flight deck. They are furthermore preprocessed, with a view to easing the task of the crews and of the maintenance personnel, by a special-purpose central computer known by various titles such as CMC standing for the expression “Central Maintenance Computer” or else CFDIU standing for “Centralized Fault Display Interface Unit”. This central maintenance computer is accessible to the crew via an interface with keyboard and screen which may be that known by the abbreviation MCDU stemming from the expression “Multipurpose Control Display Unit” but which may also be a portable computer of the PC type attached via a disconnectable data link which may or may not utilize the airplane bus. Its main function is to make, in real time or at the end of the flight, a diagnosis of the general situation of the aircraft on the basis of a summary of the fault messages received from the various pieces of equipment of the aircraft. It also fulfills other functions such as the correlating of the fault messages received with the alarms received at the flight deck level, the conducting of particular tests on the equipment, undertaken on request, by an operator intervening from the keyboard/screen interface affording access to the central maintenance computer or the compiling of a “post-flight” report, known by various titles such as PFR or LLR standing for “Post Flight Report” or “Last Leg Report”, destined for the ground maintenance teams, encompassing a log of the fault messages issued by the various pieces of equipment of the aircraft and of the alarms presented to the crew as well as the summary of the fault messages made in the last resort and more generally, all the information about the states of operation of the equipment, capable of easing the work of the ground maintenance team, whether this information results from automatic exploitation of the equipment fault messages or from remarks by the crew.
To reduce the time for which an aircraft is grounded, its equipment, be it mechanical such as valves, pumps etc., electrical such as switches, relays, batteries etc., or electronic such as automatic pilot computers, navigation computers etc., is, as often as possible, designed in such a way as to be able to be easily dismantled and replaced rapidly by standard exchange. One then speaks of LRU equipment standing for the expression “Line Replaceable Unit”.
The concept of items which can easily be dismantled and replaced by standard exchange is even extended to a lower tier of assemblage, within the pieces of equipment themselves, by use of modular architectures with modules which can easily be dismantled and replaced by standard exchange, some of them possibly being multifunction, that is to say usable in several different pieces of equipment. One then speaks of LRM modules standing for “Line Replaceable Module”.
The BITE function for testing for proper operation exists at each of the two possible levels of standard exchange of items within an aircraft: LRU equipment level and LRM equipment module level. It is referred to as the resource BITE function when it is concerned with a hardware setup or with the first-level software used (such as the operating system) and as the application BITE function when it is concerned with higher-level software. It is ensured by a piece of electronics, of which a greater or lesser hardware part tracks the fate of the item capable of a standard exchange.
The BITE function can also exist at a third level of assemblage grouping together several LRM modules placed in one and the same cabinet or rack. It is then referred to as the overall BITE function and consists of a prediagnosis easing that of the central maintenance computer.
An exemplary system for maintenance of the equipment of an aircraft by means of BITE functions integrated into the equipment and of a central maintenance computer of the aforesaid kind is described in U.S. Pat. No. 4,943,919.
Once an equipment part or a piece of equipment has been tagged as defective and removed from an aircraft, it has to be overhauled in a repair station. To ease this overhauling, it is known practice for the nonvolatile memory of the hardware part of the electronics ensuring the BITE function of the removed item, which remains integral with the item even after its removal, to be made to play an overhaul help function. Specifically, this memory which can be consulted while the item is still installed on board the aircraft, by way of the MCDU screen/keyboard interface ensuring the interface with the central maintenance computer, is also consultable in the repair station by way of a test rig specially suited to this consultation function and used to diagnose the fault.
This overhaul help resulting from the storing in memory of the diagnosis of the BITE function of the item examined is sometimes insufficient, in particular in the case of faults occurring only in a particular context. The repair technician is then required to take account of the reasons for and conditions of removal. Hitherto, these reasons for and conditions of removal have appeared in a written note drafted by the operator managing the aircraft, usually an airline company, on the basis of the notes made by the ground maintenance personnel in the aircraft's maintenance logbook (Technical/Maintenance Logbook), from indications provided by the central maintenance computer, including the “post-flight” PFR/LLR report.
This entirely manual process for advising as to the reasons for and conditions of removal of an equipment part or of a piece of equipment involving several successive intervening parties often produces retranscription errors and exaggerated simplifications in the information transmitted to the repair station, or even a complete absence of information so that the help afforded to the fault diagnosis by the note accompanying the removed item and explaining the reasons for and conditions of removal is often less than that which one would be entitled to expect.